1. Field of the Invention
The present invention relates to an image forming apparatus. More particularly, the present invention relates to an image forming apparatus that controls a home position and a plurality of color developing positions using a plurality of indication marks, and a method of detecting a home position error using the same.
2. Description of the Related Art
Generally, an electrophotographic color image forming apparatus produces a color image by forming an electrostatic latent image on a photosensitive medium charged with a uniform electrostatic potential by scanning light onto the photosensitive medium. The electrostatic latent image is developed by providing toner of a predetermined color thereto. The image developed on the photosensitive medium is transferred and fused to a printing medium. Such a color image forming apparatus typically uses four color toners, which are yellow (Y), magenta (M), cyan (C), and black (K) color toners. Therefore, four developers are needed, each of which attaches a color toner onto an electrostatic latent image.
There are two types of color image forming apparatuses. One is a single-pass type color image forming apparatus that includes four exposure units and four photosensitive media. The other type is a multi-pass type color image forming apparatus that includes a single exposure unit and a single photosensitive medium.
When a single pass type color image forming apparatus is used, it takes the same amount of time to perform color printing as does monochrome printing. Thus, the single pass color image forming apparatus performs high-speed printing. However, this type of color image forming apparatus is costly because four exposure units and four photosensitive drums are required. A multi-pass type color image forming apparatus includes a single photosensitive drum and a single exposure unit. A color toner image is formed on an intermediate transfer medium by repeating a light exposing operation, a developing operation and a transferring operation of each color. The toner color image is transferred and fused onto a printing medium. Thus, the multi-pass color image forming apparatus performs low-speed printing.
In the multi-pass type image forming apparatus, because four developers are sequentially operated, a device for consecutively transmitting a rotational force of a driving motor to the four developers is required. To do this, the conventional image forming apparatus uses four electronic clutches, and thus the image forming apparatus is expensive and bulky. Furthermore, when the clutches slip, a driving force of the driving motor cannot be timely controlled.
Accordingly, a need exists for an image forming apparatus having an indicating element with indicating units of different sizes and that detects occurrence of a home position error, thereby improving image quality.